Here is the full list of all 25 POSTAL Redux achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Perfect all Rampage levels.
Complete all Rampage levels.
Complete every level in Co-op mode.
Complete the Excess Postage campaign in Nightmare difficulty.
Complete the Campaign with a total play time of 30:00 or less.
Complete the Campaign having killed only hostiles.
Kill 30 people with the Napalm Launcher.
Execute two of every hostile type.
Earn a kill with every weapon.
Complete the Campaign.
Complete the Campaign having left no survivors.
Commit suicide.
Wipe out the game protestors in Ghetto.
Finish a level with less than 10 health.
Kill all Ostriches in The Farm.
Kill three or more people with a single Mine explosive.
Reach the half way mark of the Campaign.
Blow up 50 barrels.
Kill four or more people with a single Rocket Launcher missile.
Firebomb the Marching Band.
Perform 13 executions.
Duck under 10 rockets.
When burning, set someone else on fire by running into them.
Make your first kill.
Watch the entire credit sequence.